A. Field of the Invention
The present invention relates to an endoscope comprising a solid-state image sensor in a distal end portion of an insertion section thereof.
B. Description of the Prior Art
An endoscope is known which has a solid-state image sensor in a distal end portion of an insertion section and allows observation of a body cavity in cooperation with the image sensor and an image reproduction apparatus.
A typical example of an endoscope with a solid-state image sensor is disclosed in Japanese Patent Disclosure (Kokai) No. 60-258515. The endoscope disclosed in this prior art comprises an objective optical system, a prism, and a solid-state image sensor. All beams reflected by a portion to be examined and incident on the objective optical system are reflected by the prism in a direction substantially perpendicular to the optical axis of the objective optical system and are guided to one side surface of the solid-state image sensor.
A flat circuit board is bonded to the other side surface of the solid-state image sensor. A large number of electronic components are mounted on the circuit board for amplifying an image signal sent from the solid-state image sensor, and for partially generating a solid-state image sensor driving pulse, and for adjusting a time lag between the solid-state image sensor driving pulse and an image output signal from the solid-state image sensor.
In a conventional endoscope having the structure described above, the electronic components having predetermined sizes are mounted on the flat circuit board, and the diameter of the distal end portion of the insertion section of the endoscope is inevitably increased.
In order to mount many electronic components on the circuit board, the board must be elongated along the axial direction of the insertion section. Therefore, the hard distal end portion of the insertion section of the endoscope is elongated accordingly.
When the distal end portion of the insertion section of the endoscope is enlarged and elongated, insertion of the insertion section into a body cavity causes great pain to the patient.